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What is Magnesium Sulfate?

By Helga George
Updated May 21, 2024
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Magnesium sulfate is a sulfur salt of magnesium that has many medical uses, and is frequently used as a fertilizer. It occurs in both an anhydrous form — meaning 'lacking water' — and in several forms in which it is combined with water molecules. One of these forms is the commonly used bath additive known as Epsom Salts.

Magnesium is an important co-factor for over 300 enzymatic reactions in humans. It is particularly important for the transmission of signals in the nerves and the excitability of muscles. It is also required for the biochemical reactions leading to DNA and RNA synthesis.

The magnesium sulfate formula is MgSO4, so it also contains oxygen in addition to magnesium and sulfur. The anhydrous form has a molecular weight of 120.4 grams per molecule (g/mol). It is very absorbent of water, readily obtaining it from the air. This tendency makes it a useful drying agent, and it is used in organic chemistry to remove water from organic solutions.

The most commonly used forms are hydrated magnesium sulfate, or molecules that are combined with water. For instance, the formula for Epsom Salts is MgSO4.7H20. This is known as a heptahydrate, because it has seven water molecules associated with it. This form of magnesium sulfate is very stable, and is often used for medical purposes. It has a pH of 5.5-6.5, a molecular weight of 246.5, and is water soluble.

One of the most widespread uses of the heptahydrate form is intravenously (IV) to treat severe ecclampsia in pregnant women. There is debate about the value of using this to treat pre-ecclampsia. Recent studies have found that giving this treatment to women at high risk for giving birth prematurely significantly reduces the chances of the children having cerebral palsy.

IV-administered magnesium sulfate heptahydrate is also used to treat convulsions caused by epilepsy, and other forms of seizures. In children, its use should be restricted to seizures that are life-threatening. There can be complications with kidney function when magnesium sulfate is used, so doctors need to monitor renal function.

Hypomagnesia is a condition in which the blood has atypically low levels of magnesium. This refers solely to the levels in the blood. One can have this condition without having an overall deficiency of magnesium in the body. Treatment with the IV heptahydrate form is also used for this condition.

Water-based solutions of magnesium sulfate are used as a laxative, and Epsom Salts are highly favored as bathing salts. They are used to rejuvenate sore muscles, treat back pain, and to recover from the pain of childbirth. Bathing in them can also help alleviate the pain of herpes viruses, such as shingles and genital herpes.

Magnesium sulfate is also frequently used as a plant fertilizer. Plants utilize chlorophyll to carry out photosynthesis, and chlorophyll has magnesium at its center. The heptahydrate form is more soluble than other types of magnesium, so it makes a more desirable fertilizer.

Another use for this compound is to treat to the water in marine aquaria that have a lot of stony corals. This is beneficial because, as corals calcify, they deplete the levels of magnesium in the water. The heptahydrate form maintains necessary magnesium levels.

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Discussion Comments
By anon927605 — On Jan 25, 2014

How much, or what portion or percentage, of elemental pure magnesium is in magnesium-sulfate (or Epsom salts)? And what is this requested measurement generally called?

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